Digestive System: Structure and Function of Exchange Surfaces in Multicellular Organisms

Heterotrophs

Organisms that obtain energy by using the organic molecules present in food.

Ingestion

Intake of food.

Digestion

Breakdown of molecules.

Absorption

Uptake of nutrients into blood or lymph.

Defecation/Egestion

Elimination of undigested material.

Mechanical Digestion

Breaking down food into smaller pieces when force is applied.

Chemical Digestion

Enzymes are involved to break down food into small, water-soluble molecules.

Amylase

Enzyme that breaks down starch (polysaccharide) to maltose (disaccharide).

Peristalsis

An involuntary muscle contraction that moves food along the oesophagus.

Pepsin

Enzyme produced in the stomach that breaks down proteins to polypeptides.

Hydrochloric Acid

Substance produced in the stomach to maintain an optimum pH of 2 for pepsin to work.

Maltase

Enzyme that converts maltose to glucose.

Peptidase

Enzyme that converts polypeptides to amino acids.

Lipase

Enzyme that converts lipids to fatty acids and glycerol.

Villi

Exchange surface in the digestive system located in the small intestine.

Gall Bladder

Stores bile produced in the liver, which breaks down lipids.

Pancreas

Produces enzymes and bicarbonate solution which restores the pH to 7.

Small Intestine

Receives fluids from the gall bladder and pancreas and is involved in nutrient absorption.

Incisors

Teeth used to cut food.

Canines

Teeth used to tear food.

Molars

Teeth used to grind food.

Pre-molars

Teeth used to grind food.

Amino acids

Organic compounds that serve as the building blocks of proteins.

Glucose

A simple sugar that is an important energy source in living organisms.

Microvilli

Tiny projections on the surface of villi that further increase the surface area for absorption.

Large Intestine

Part of the digestive system where water is absorbed from cellulose, making remains solid.

Fibre

Indigestible material, such as cellulose, that humans cannot break down.

Caecum

An offshoot from the large intestine with no function in humans.

Appendix

An offshoot from the large intestine with no function in humans.

Salivary gland

Gland that secretes saliva containing enzymes to begin the digestion of starch.

Oesophagus

Tube that transports partly digested food from the mouth to the stomach.

Stomach

Organ that secretes gastric juice containing hydrochloric acid and enzymes for protein digestion.

Liver

Organ that produces bile, which is stored in the gall bladder.

Duodenum

First part of the small intestine that secretes enzymes to complete digestion.

Ileum

Last part of the small intestine that absorbs most small, water-soluble products of digestion.

Colon

Part of the large intestine that absorbs water, minerals, and some vitamins.

Rectum

Part of the large intestine that stores indigestible food material before elimination.

Gastric juice

Liquid secreted by the stomach containing hydrochloric acid and enzymes.

Pancreatic juice

Liquid secreted by the pancreas containing enzymes for digestion.

Bile

Liquid produced by the liver that aids in the digestion of fats.